This invention relates generally to semiconductor devices and, more particularly, to the internal wiring of semiconductor devices such as a power transistor module.
Typically, a power transistor module includes a circuit assembly mounted on an insulative substrate which is enclosed in a case having a lid in the form of a terminal block through which external lead-through terminals extend and are connected to terminal connections of the circuit assembly. A typical construction of a power transistor module, illustrated in FIG. 5 without the usual case, includes a metallic substrate 1, which serves as a heat-dissipating plate and may also form the bottom of the case, on which is mounted an insulative substrate 2. Formed on the insulative substrate is a circuit assembly including conductor patterns 3 which interconnect semiconductor components including transistor chips 4 (e.g., Darlington pairs) and diodes 5. The electrodes of the transistor chips 4 are connected by bonding wires 6 to the conductor patterns 3. In the illustrated example, the equivalent circuit of which is shown in FIG. 4, two sets of semiconductor chips are connected in parallel to increase the current carrying capacity of the circuit assembly.
Connection to the circuit assembly is made via a series of main external lead-through terminals 9 and a series of auxiliary external lead-through terminals 10 which extend through an insulative terminal block 7, formed of resin, for example. The terminal block is superposed on the circuit substrate assembly and lead-through terminals 9 and 10 are soldered by means of reflow soldering to the terminal connections of the conductor patterns 3 on the substrate. The resulting assembly of the terminal block with the metallic substrate and the circuit substrate assembly is then assembled in a case, with terminal block 7 serving as the lid, and filled with a resin gel filler material to seal the case and complete the semiconductor device.
Each of the external lead-through terminals 9 and 10 on terminal block 7 is made by pressing and bending processes, with the bent tips at the inner ends all aligned in the same plane and the legs pressed into the case lid 7. Circuit locations requiring internal connection between the external lead-through terminals 9 and 10 are wired together with insulation covered leads 11.
Among the disadvantages of the internal wiring structure of the described semiconductor device is that the external lead-through terminals 9 and 10 are fabricated piece-by-piece as individual parts having different shapes, which contributes to poor material yield. In order to reliably solder the superposed terminal block 7 to the conductor patterns 3 on the circuit substrate, it is necessary for the tips of the legs of each lead-through terminal to be aligned very accurately, as the external lead-through terminals 9 and 10 are individually pressed into the case lid 8. The process control necessary to assure flatness of the finished module is complex and difficult to perform.
The use of flexible leads 11 for part of the internal wiring of the module dictates the use of tedious hand work, which is not only labor intensive but may result in inconsistencies in the length and routing of the leads which makes the semiconductor device susceptible to an induction effect from the main circuit current. Also, the hand-soldered connections may become loosened, causing undesirable oscillations and malfunction of the circuit.
A primary object of the present invention is to overcome the described problems of prior module structures and methods for their fabrication.
A more specific object is to provide an internal wiring structure for a semiconductor device which eliminates the need for internal leads that can cause oscillations and circuit malfunction.
Another object of the invention is to provide an improved internal wiring structure which simplifies the assembly, and increases the material yield, of a power transistor module.